A variety of catalysts for hydrotreating, hydrodesulfurization, and/or hydrodenitrogenation are known and/or are commercially available. Some of these catalysts contain molybdenum, nickel or cobalt, and phosphorus. Some impregnation solutions from which such catalysts are made have molybdenum present in concentrations up to about 550 g/L (expressed as MoO3), i.e., about 3.8 mol/L. In this connection, U.S. Pat. No. 7,361,624 discloses catalysts in which the loading is such that the Group VI metal (as its trioxide) is 10 to 30 wt % of the catalyst. U.S. Pat. No. 5,164,354 suggests that catalyst having 5 to 50 wt % Group VI metal on the support can be prepared; in Example I therein, two impregnation steps were needed to achieve 26.2 wt % molybdenum on the support. Impregnation solutions having 45 to 80 grams of molybdenum trioxide, 8 to 20 grams of nickel oxide, and zero to 15 grams of cobalt oxide in 100 mL of solution have been reported in CN 1172692. Because these types of catalysts are usually prepared by pore volume impregnation, the amount of hydrogenation metals in solution determines the amount of hydrogenation metals on the support. To increase the loading of hydrogenation metals on the support, multiple sequential impregnation steps are usually employed. Impregnation solutions having higher concentrations of hydrogenation metals are desired, so that catalysts with higher loadings can be prepared in a single impregnation step.